Skandapurana 16.29.4

16.29.4

ādau kṛtvā tu vapanaṃ someśvarasamīpataḥ ..
śaṃkaraṃ manasā dhyāyankeśāṃstatra parityajet ..
samuttārya tataḥ keśānbhūyaḥ snānaṃ samācaret .. 4 ..

having first performed shaving near Someśvara; / meditating on Śaṃkara in one’s mind, one should cast off one's hair there; / having removed the hair, one should then perform ritual ablution again.